The present invention relates to the preparation and use of rotating element sheet material with a generalized containment structure. Specifically, the present invention relates to the preparation and use of rotating element sheet material with a matrix substrate, or a substrate derived from a matrix structure.
Rotating element sheet material has been disclosed in U.S. Pat. Nos. 4,126,854 and 4,143,103, both herein incorporated by reference, and generally comprises a substrate, an enabling fluid, and a class of rotatable elements. As discussed more below, rotating element sheet material has found a use as xe2x80x9creusable electric paper.xe2x80x9d FIG. 1 depicts an enlarged section of rotating element sheet material 18, including rotatable element 10, enabling fluid 12, cavity 14, and substrate 16. Observer 28 is also shown. Although FIG. 1 depicts a spherically shaped rotatable element and cavity, many other shapes will work and are consistent with the present invention. As disclosed in U.S. Pat. No. 5,389,945, herein incorporated by reference, the thickness of substrate 16 may be of the order of hundreds of microns, and the dimensions of rotatable element 10 and cavity 14 may be of the order of 10 to 100 microns.
In FIG. 1, substrate 16 is an elastomer material, such as silicone rubber, that accommodates both enabling fluid 12 and the class of rotatable elements within a cavity or cavities disposed throughout substrate 16. The cavity or cavities contain both enabling fluid 12 and the class of rotatable elements such that rotatable element 10 is in contact with enabling fluid 12 and at least one translational degree of freedom of rotatable element 10 is restricted. The contact between enabling fluid 12 and rotatable element 10 breaks a symmetry of rotatable element 10 and allows rotatable element 10 to be addressed. The state of broken symmetry of rotatable element 10, or addressing polarity, can be the establishment of an electric dipole about an axis of rotation. For example, it is well known that small particles in a dielectric liquid acquire an electrical charge that is related to the Zeta potential of the surface coating. Thus, an electric dipole can be established on a rotatable element in a dielectric liquid by the suitable choice of coatings applied to opposing surfaces of the rotatable element.
The use of rotating element sheet material as xe2x80x9creusable electric paperxe2x80x9d is due to that fact that the rotatable elements are typically given a second broken symmetry, a multivalued aspect, correlated with the addressing polarity discussed above. That is, the above mentioned coatings may be chosen so as to respond to incident electromagnetic energy in distinguishable ways. Thus, the aspect of rotatable element 10 to observer 28 favorably situated can be controlled by an applied vector field.
For example, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, rotatable element 10 may comprise a black polyethylene generally spherical body with titanium oxide sputtered on one hemisphere, where the titanium oxide provides a light-colored aspect in one orientation. Such a rotatable element in a transparent dielectric liquid will exhibit the desired addressing polarity as well as the desired aspect.
A multivalued aspect in its simplest form is a two-valued aspect. When the aspect is the chromatic response to visible light, a rotatable element with a two-valued aspect can be referred to as a bichromal rotatable element. Such a rotatable element is generally fabricated by the union of two layers of material as described in U.S. Pat. No. 5,262,098, herein incorporated by reference.
FIGS. 2-5 depict rotatable element 10 with a two-valued aspect and an exemplary system that use such rotatable elements from the prior art. In FIG. 2, rotatable element 10 is composed of first layer 20 and second layer 22 and is, by way of example again, a generally spherical body. The surface of first layer 20 has first coating 91 at a first Zeta potential, and the surface of second layer 22 has second coating 93 at a second Zeta potential. First coating 91 and second coating 93 are chosen such that, when in contact with a dielectric fluid (not shown), first coating 91 has a net positive electric charge with respect to second coating 93. This is depicted in FIG. 2 by the xe2x80x9c+xe2x80x9d and xe2x80x9cxe2x88x92xe2x80x9d symbols respectively. Furthermore, the combination of first coating 91 and the surface of first layer 20 is non-white-colored, indicated in FIG. 2 by hatching, and the combination of second coating 93 and the surface of second layer 22 is white-colored. One skilled in the art will appreciate that the material associated with first layer 20 and first coating 91 may be the same. Likewise, the material associated with second layer 22 and second coating 93 may be the same.
FIG. 3 depicts no-field set 30. No-field set 30 is a subset of randomly oriented rotatable elements in the vicinity of vector field 24 when vector field 24 has zero magnitude. Vector field 24 is an electric field. No-field set 30, thus, contains rotatable elements with arbitrary orientations with respect to each other. Therefore, observer 28 in the case of no-field set 30 registers views of the combination of second coating 93 and the surface of second layer 22, and first coating 91 and the surface of first layer 20 (as depicted in FIG. 2) in an unordered sequence. Infralayer 26 forms the backdrop of aspect 34. Infralayer 26 can consist of any type of material, including but not limited to other rotatable elements, or some material that presents a given aspect to observer 28.
FIGS. 4 and 5 depict first aspect set 32. First aspect set 32 is a subset of rotatable elements in the vicinity of vector field 24 when the magnitude of vector field 24 is nonzero and has the orientation indicated by arrow 25. In first aspect set 32, all of the rotatable elements orient themselves with respect to arrow 25 due to the electrostatic dipole present on each rotatable element 10. In contrast to no-field set 30, observer 28 in the case of first aspect set 32 registers a view of a set of rotatable elements ordered with the non-white-colored side up (the combination of first coating 91 and the surface of first layer 20 as depicted in FIG. 2). Again, infralayer 26 forms the backdrop of the aspect. In FIGS. 4 and 5, rotatable element 10, under the influence of applied vector field 24, orients itself with respect to vector field 24 due to the electric charges present as a result of first coating 91 and second coating 93. FIG. 4 is a side view indicating the relative positions of observer 28, first aspect set 32, and infralayer 26. FIG. 5 is an alternate view of first aspect set 32 from a top perspective. In FIG. 5, the symbol "THgr" indicates an arrow directed out of the plane of the figure.
One skilled in the art will appreciate that first aspect set 32 will maintain its aspect after applied vector field 24 is removed, in part due to the energy associated with the attraction between rotatable element 10 and the substrate structure, as, for example, cavity walls (not shown). This energy contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 18, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, and discussed in more detail below.
A rotatable element with multivalued aspect is generally fabricated as disclosed in U.S. Pat. No. 5,919,409, herein incorporated by reference. An exemplary rotatable element 10 with multivalued aspect of the prior art is depicted in FIG. 6. Rotatable element 10 in FIG. 6 is composed of first layer 36, second layer 37 and third layer 38. The surface of third layer 38 has third coating 95 at a first Zeta potential, and the surface of first layer 36 has first coating 94 at a second Zeta potential such that third coating 95 has a net positive charge, xe2x80x9c+,xe2x80x9d with respect to first coating 94 when rotatable element 10 is in contact with a dielectric fluid (not shown). First layer 36, first coating 94, third layer 38, and third coating 95 may be chosen to be transparent to visible light and second layer 37 may be chosen to be opaque or transparent-colored to visible light, such that the rotatable element acts as a xe2x80x9clight-valve,xe2x80x9d as disclosed, for example, in U.S. Pat. No. 5,767,826, herein incorporated by reference, and U.S. Pat. No. 5,737,115, herein incorporated by reference. As above, one skilled in the art will appreciate that the material associated with first layer 36 and first coating 94 may be the same. Likewise, the material associated with third layer 38 and third coating 95 may be the same.
Rotatable elements with multivalued aspect are generally utilized in rotating element sheet material that use canted vector fields for addressing. A canted vector field is a field whose orientation vector in the vicinity of a subset of rotatable elements can be set so as to point in any direction in three-dimensional space. U.S. Pat. No. 5,717,515, herein incorporated by reference, discloses the use of canted vector fields in order to address rotatable elements. The use of canted vector fields with rotating element sheet material allows complete freedom in addressing the orientation of a subset of rotatable elements, where the rotatable elements have the addressing polarity discussed above.
One skilled in the art will appreciate that no-field set and first aspect set discussed above in FIGS. 3-5 can form the elements of a pixel, where vector field 24 can be manipulated on a pixel by pixel basis using an addressing scheme as discussed, for example, in U.S. Pat. No. 5,717,515, hereinabove incorporated by reference.
As discussed above, a useful property of rotating element sheet material is the ability to maintain a given aspect after applied vector field 24 for addressing is removed. This ability contributes, in part, to the switching characteristics and the memory capability of rotating element sheet material 18, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference. This will be referred to as aspect stability. The mechanism for aspect stability in the above embodiments is generally the energy associated with the attraction between the rotatable elements and the containment structure, or xe2x80x9cwork function.xe2x80x9d A host of factors influence the magnitude of the energy associated with the work function including, but not limited to: surface tension of enabling fluid in contact with rotatable elements; the relative specific gravity of the rotatable elements to the enabling fluid; magnitude of charge on rotatable elements in contact with containment structure; relative electronic permittivity of enabling fluid and containment structure; xe2x80x9cstickinessxe2x80x9d of containment structure; and other residual fields that may be present. The applied vector field for addressing must be strong enough to overcome the work function in order to cause an orientation change; furthermore, the work function must be strong enough to maintain this aspect in the absence of an applied vector field for addressing.
FIG. 7 depicts an exemplary diagram of number 54, N, of rotatable elements that change orientation as a function of applied vector field 24, V of the prior art. The work function 52, Vw, corresponds to the value of applied vector field 24 when the number 54 of rotatable elements that change orientation has reached the saturation level 56, Ns, corresponding to the orientation change of all rotatable elements 10.
As mentioned above in connection with FIG. 1, the substrate of rotating element sheet material is generally an elastomer material such as silicone rubber. Because of the expense of silicone rubber, the substrate is currently the most expensive component of rotating element sheet material. Thus, in large-area-display applications of rotating element sheet material, the cost of the substrate is the primary impediment. Other qualities of rotating element sheet material, however, are ideally suited to large-area-display applications. Such qualities include: lack of sensitivity to uniform thickness, low power requirements, and a wide viewing angle.
One option that is available for large-area-display applications using rotating element sheet material without a silicone rubber substrate is based on the disclosure of U.S. Pat. No. 5,825,529, herein incorporated by reference (the ""529 patent). The rotatable elements in the ""529 patent are supported by neighboring rotatable elements in a packed relationship. However, because of the proximity of other rotatable elements with an addressing polarity, and the limited contact with a containment structure, the work function associated with an aspect of the rotating element sheet material disclosed in the ""529 patent is less pronounced than in rotating element sheet material with a cavity-containing substrate. Thus, it remains desirable to fabricate rotating element sheet material with a generalized containment structure that exhibits a suitable work function.
Accordingly, in a first embodiment of the present invention, rotating element sheet material comprises a fibrous matrix and a plurality of rotatable elements, where the plurality of rotatable elements are disposed within the fibrous matrix and in contact with an enabling fluid.
In a second embodiment of the present invention, rotating element sheet material comprises a fibrous matrix, a plurality of micro-capsules, and a plurality of rotatable elements, where each of the plurality of micro-capsules contain a subset of the plurality of rotatable elements and an enabling fluid. Furthermore, an additional supporting material may be interstitially contained in the fibrous matrix.
In a first embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises dispersing a plurality of rotatable elements into pulp slurry, drying and pressing thin layers of the pulp slurry into a fibrous matrix where the plurality of rotatable elements are interstitially contained, and infusing the fibrous matrix with an enabling fluid.
In a second embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises encapsulating a plurality of rotatable elements and enabling fluid into a plurality of micro-capsules, dispersing the plurality of micro-capsules into pulp slurry, drying and pressing thin layers of the pulp slurry into a fibrous matrix where the plurality of micro-capsules are interstitially contained. Furthermore, an additional supporting material may be introduced to the interstitial regions of the fibrous matrix.
In a third embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises pressing thin layers of pulp slurry into a fibrous matrix sheet, embossing cavities of size suitable to contain, preferably, single rotatable elements onto the surface of the fibrous matrix sheet using a mechanical embossing tool incorporating heat and pressure as needed, and subsequently drying the fibrous matrix sheet. Next, the rotatable elements are introduced to the embossed cavities by any conventional means known in the art, the fibrous matrix sheet is infused with enabling fluid, and the embossed cavities are sealed by laminating a second fibrous matrix sheet over the embossed fibrous matrix sheet. Alternatively, the embossed cavities are sealed by applying windowing material, such as glass or plastic sheets, to the embossed fibrous matrix sheet containing the rotatable elements in the embossed cavities. Also, and again alternatively, the embossed cavities can be introduced into dried fibrous matrix sheets using heat and pressure as required, and subsequently introducing the rotatable elements by any conventional means known in the art.
In a fourth embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises pressing thin layers of pulp slurry into a fibrous matrix sheet, embossing cavities of size suitable to contain, preferably, single micro-capsules containing one or more rotatable elements and enabling fluid, onto the surface of the fibrous matrix sheet using a mechanical embossing tool incorporating heat and pressure as needed, and subsequently drying the fibrous matrix sheet. Next, the micro-capsules are introduced to the embossed cavities by any conventional means known in the art, and the embossed cavities are sealed by laminating a second fibrous matrix sheet over the embossed fibrous matrix sheet. Alternatively, the embossed cavities are sealed by applying windowing material, such as glass or plastic sheets, to the embossed fibrous matrix sheet containing the micro-capsules in the embossed cavities. Also, and again alternatively, the embossed cavities can be introduced into dried fibrous matrix sheets using heat and pressure as required, and subsequently introducing the micro-capsules by any conventional means known in the art. Furthermore, an additional supporting material may be introduced to the interstitial regions of the fibrous matrix.
In a fifth embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises weaving a fibrous matrix sheet using a loom or other method of rapidly creating a fabric that enables placement of fibers in preferred patterns, where the preferred pattern in this embodiment defines preferred interstitial regions. Rotatable elements are subsequently introduced to the preferred interstitial regions of the fibrous matrix sheet by any conventional means known in the art, the fibrous matrix sheet is infused with enabling fluid, and further laminated by another sheet or windowing material, as previously described. Alternatively, the plurality of rotatable elements may be placed in a preferred spatial configuration with respect to one another and a plurality of fibers or fibrous material introduced, by electrostatic or other means, to randomly encapsulate the rotatable elements. The plurality of fibers or fibrous material thus arranged constitutes the desired fibrous matrix. The fibrous matrix is then infused with enabling fluid, and further laminated by another sheet or windowing material, as previously described.
Further still, in a sixth embodiment of a method for assembling rotating element sheet material, and the rotating element sheet material so produced, the method comprises weaving a fibrous matrix sheet using a loom or other method of rapidly creating a fabric that enables placement of fibers in preferred patterns, where the preferred pattern in this embodiment defines preferred interstitial regions. Micro-capsules containing one or more rotatable elements and enabling fluid, are subsequently introduced to the preferred interstitial regions of the fibrous matrix sheet by any conventional means known in the art and the fibrous matrix sheet is laminated by another sheet or windowing material, as previously described. Alternatively, the plurality of micro-capsules may be placed in a preferred spatial configuration with respect to one another and a plurality of fibers or fibrous material introduced, by electrostatic or other means, to randomly encapsulate the micro-capsules. The plurality of fibers or fibrous material thus arranged constitutes the desired fibrous matrix. The fibrous matrix is then laminated by another sheet or windowing material, as previously described. Furthermore, an additional supporting material may be introduced to the interstitial regions of the fibrous matrix.